1. Field of Invention
This invention relates to hydraulic systems and more particularly to a hydraulic system manifold and a volumetric compensator.
2. Description of Related Art
Hydraulic linear actuators are well known and widely used in industry. In contrast to electromechanical actuators, they are more practical and reliable in applications requiring a large, controllable force. A double-acting hydraulic linear actuator applies such force both in extension and in retraction.
Conventionally, a hydraulic linear actuator is connected to a remote supply of pressurized hydraulic fluid through a closed network of pipes and control valves. However, those are applications where it is desirable for a hydraulic linear actuator to be freestanding and mobile, having a prime mover, a pump, and a closed hydraulic fluid control system all integrated with and located proximate to the linear actuator. Such freestanding actuators are particularly suitable for vehicular applications, such as on automobiles and aircraft.
Prior art freestanding hydraulic actuators are disclosed in U.S. Pat. No. 2,640,323 and 2,640,426 to Stewart B. McLeod and U. S. Pat. No. 5,144,801 to Dino Scanderbeg et al.
It appears that the devices disclosed in each of these references use a reservoir to supply a pump with hydraulic fluid and, where unbalanced cylinders (single rod cylinders) are used, the reservoir absorbs excess hydraulic fluid ejected from the cylinder during rod retraction. Disadvantageously, fluid in a reservoir flows in response to gravitational force, and thus the orientation of the reservoir and the actuator at large may be constrained. If a reservoir-type actuator is improperly oriented, the pump may not be properly supplied with fluid and cavitation may result. Furthermore, generally, a reservoir-type actuator requires more hydraulic fluid to reduce the risk of cavitation.
Conventional freestanding hydraulic linear actuators do not provide for load locking, except through operation of the prime mover. Locking the actuator in position to support a load requires that sufficient fluid pressure be maintained in the actuator cylinder to support the rod. Convention al freestanding hydraulic linear actuators do not normally have the necessary valve configuration to accomplish this task, and thus depend on the prime mover to maintain fluid pressure for load locking.
Thus, there is a need for a way to provide a reservoir-less, freestanding, hydraulic linear actuator that can be operated in any orientation, independent of gravitational forces and which provides for load locking without the operation of a prime mover.
The above problems in the prior art are addressed by providing a hydraulic system manifold comprising a body, a counterbalancer in the body and a flow controller in the body. The body has first and second pump ports, first and second cylinder ports, first and second compensator ports and first and second supply conduits in communication with the first and second pump ports, the counterbalancer and the flow controller. The counterbalancer is in communication wit h the first and second supply conduits and th e cylinder ports, to communicate hydraulic fluid between the first and second supply conduit s and the first and second cylinder ports while counterbalancing hydraulic fluid pressure in th e first and second supply conduits. The flow controller is in communication with the first and second supply conduits and the compensator ports, to control the flow of hydraulic fluid between the compensator ports and the first and second supply conduits to supply and store hydraulic fluid in a volumetric compensator in communication with the compensator ports.
The counterbalancer may comprise first and second cross piloted counterbalance valves. The first cross piloted counterbalance valve may be connected between the first supply conduit and the first cylinder port and the second cross piloted counterbalance valve may be connected between the second supply conduit and the second cylinder port such that a fraction of hydraulic pressure in the first supply conduit is operable to actuate the second cross piloted counterbalance valve to permit fluid to flow from the second cylinder port to the second supply conduit and such that a fraction of hydraulic pressure in the second supply conduit actuates the first cross piloted counterbalance valve to permit fluid to flow from the first cylinder port to the first supply conduit.
Preferably, the first and second cross piloted counterbalance valves are independently thermally actuated to permit hydraulic fluid flow from the first and second cylinder ports to the first and second supply conduits respectively, when the temperature of hydraulic fluid at a corresponding one of the cylinder ports exceeds a value.
The flow controller may include first and second cross piloted check valves. The first cross piloted check valve may be in communication with the first supply conduit and the first compensator port and the second cross piloted check valve may be in communication with the second supply conduit and the second compensator port. The first cross piloted check valve may be actuated by a fraction of hydraulic pressure in the second supply conduit to permit fluid to flow from the first supply conduit to the first compensator port and the second cross piloted check valve may be actuated by a fraction of hydraulic pressure in the first supply conduit to permit fluid to flow from the second supply conduit to the second compensator port.
Preferably, first and second pressure relief valves are connected in opposite directions between the first and second supply conduits respectively.
The body may have a pump mount for removably mounting a hydraulic fluid circulating pump to the body for communication with the first and second pump ports. The body may also have a cylinder mount for removably mounting a hydraulic cylinder in communication with the first and second cylinder ports. The body may also have a volumetric compensator mount for removably mounting the volumetric compensator in communication with the first and second compensator ports.
A hydraulic system may be formed by a hydraulic cylinder mounted to the body in communication with the first and second cylinder ports, a hydraulic circulating pump mounted to the body in communication with the first and second pump ports, and a volumetric compensator mounted to the body in communication with the first and second volumetric compensator ports.
The volumetric compensator may have a housing having an opening for communicating with the first and second compensator ports to receive and expel hydraulic fluid, a flexible diaphragm member defining an expandable volume within the housing and in communication with the openings to receive hydraulic fluid therein, and a counterforce provider, for providing a counterforce on the flexible diaphragm member, tending to reduce the expandable volume.
The counterforce provider may comprise a spring acting between the housing and the flexible diaphragm member.
Preferably the volumetric compensator has a mount for removably mounting the housing to the hydraulic system manifold such that the opening is in communication with first and second compensator ports of the manifold.
Other aspects and features of the present invention will become apparent to those ordinary skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.